电缆振荡波试验中直流充电速率对XLPE中空间电荷积聚的影响

Effect of Charge Rate on Space Charges Accumulation in XLPE in Damped Alternating Current Testing for Power Cable

振荡波（DAC）测试广泛应用于35 k V及以下电压等级电缆的局部放电检测中,但这种方法目前在更高电压等级（110 k V及以上）电缆中的应用较少,其中一个原因是人们担心直流充电过程可能造成空间电荷的累积,从而危及电缆绝缘。为此,基于电声脉冲（PEA）法测量了不同直流充电速率下XLPE材料中的空间电荷量,并进行了比较分析。制备了厚度为0.35 mm、大小为40 mm×40 mm的XLPE试样,分别线性升压至12、20、30 k V/mm场强,并维持40 min,以空间电荷密度为特征量,分析了线性升压阶段、维持电压阶段以及去压过程中空间电荷分布的变化。结果表明：在线性升压过程中,即充电速率很慢时,XLPE中空间电荷不易积聚;当所加电压的场强〈12 k V/mm时,即达不到电荷注入场强阈值时,空间电荷也不易积聚;电压恒定并维持一段时间后,XLPE中的空间电荷才开始不断积聚。

Damped alternating current（DAC） testing is widely used for partial discharge detection of grade 35 k V-and-below cables, but this method is currently used less frequently in higher-voltage grade（110 k V and above） cables. One of the reasons is that people worry about the DC charging process may cause the accumulation of space charge, thus endangering the cable insulation. Consequently, by the pulsed electroacoustic（PEA） method, we measured and compared the space charges in XLPE materials at different DC charging rates. XLPE specimens with a thickness of 0.35 mm and a size of 40 mm×40 mm were prepared and were linearly applied to 12 k V/mm, 20 k V/mm and 30 k V/mm field strengths and maintained for 40 min. The change in the space charge distribution was analyzed during the linear voltage stage, the sustain voltage stage, and the voltage off process. The results show that, in the linear voltage process, even the charge rate is very slow, the space charge in the XLPE is not easy to accumulate; if the applied voltage field is too low, which is beyond 12 k V/mm and unable to reach the threshold of the injected field strength, the space charge is not easy to accumulate. If the voltage is constant and maintained for a period of time, the space charge in the XLPE begins to accumulate.